The present invention relates to disk drives and storage devices. In particular, the present invention relates to reducing undesirable audible noise in velocity controlled hard disk drive head/arm assemblies during head retraction.
Generally, a magnetic hard disk drive (HDD) includes a magnetic read/write head and several magnetic disks, each disk having concentric data tracks for storing data. The disks are mounted on a spindle motor, which causes the disks to spin. The read/write head is typically mounted on a slider, which is mounted to a suspension or load beam. The load beam is attached to an actuator arm of an actuator, which moves the read/write head over the spinning disk during operation. As the disks spin, the slider suspended from the actuator arm “flies” a small distance above the disk surface. The slider carries a transducing head for reading from or writing to a data track on the disk.
In addition to the actuator arm, the slider suspension comprises a bearing about which the actuator arm pivots. A large scale actuator motor, such as a voice coil motor (VCM), is used to move the actuator arm (and the slider) over the surface of the disk. When actuated by the VCM, the actuator arm can be moved from an inner diameter to an outer diameter of the disk along an arc until the slider is positioned above a desired data track on the disk.
A control circuit is coupled to a coil in the VCM in order to controllably supply current to the coil. When a current is passed through the coil, a motive force is exerted on the actuator arm. The actuator arm is subjected to a force tending to accelerate the actuator arm at a rate defined by the magnitude of the current, and in a direction defined by the polarity of the current. Thus, in order to accelerate or decelerate the actuator arm until it is moving at a desired velocity and in a desired direction, it is important to know the actual direction and velocity of the actuator arm. It is known that the back electromotive force (back EMF) from the coil of the actuator is representative of the velocity and direction of movement of the actuator arm.
Parking zones in an HDD allow the read/write head to be safely landed after the hard drive has ceased operation. When an HDD is powered down, it usually performs certain operations before actually disconnecting from the external power source. One of these power down operations is to operate the actuator arm to move the head to the parking zone. If the head is not moved to the parking zone prior to power down, the head will land on the disk after the disk stops spinning, potentially damaging the disk and the read/write head.
In many conventional systems, the drive voltage or current to the VCM is continuously enabled and disabled at a constant frequency in order to provide alternating driving of the VCM (enabled) and measuring of the actuator arm speed by the control circuitry (disabled). The frequency of the drive voltage or current in these systems is typically at a frequency within the audible range, thereby causing an undesirable constant tone during head retraction. One method of resolving this problem is to limit the magnitude of the drive to the VCM to keep the acoustic noise level to a minimum. However, by limiting the maximum drive to keep the acoustic level low, the speed of the retraction cannot be controlled as easily. This is especially true when the read/write head reaches the parking zone or when a retraction magnet accelerates the actuator arm.
Thus, there is a need for an actuator arm retract controller that reduces audible noise while still allowing velocity control of the actuator arm during retraction.